let input = document.querySelector("#app input");
document.querySelector("#hd").insertAdjacentElement("afterbegin", input);
input.setAttribute("value", "ok...");
input.style.height = "100px";

内存中管理节点;
const elements = document.createDocumentFragment();
elements.appendChild(input);
input.style.cssText = `height:100px; border:solid 10px red;`;
document.querySelector("#app").appendChild(elements);
